1. Field of the Invention
The present invention relates to an oxygen barrier resin composition and a product containing the same. More particularly, the present invention relates to the use of a compatibilizer in compounding an ethylene-vinyl alcohol copolymer (hereinafter referred to as "EVOH") with an ethylene copolymer, thereby providing good appearance, oxygen barrier and mechanical properties to molded properties to molded products.
2. Description of the Prior Art
Resins based on polyolefins, such as polyethylene and polypropylene, are widely used in various fields by virtue of their superior moldability, mechanical properties and moisture barrier. They are also highly permeable to gas, but this acts to limit the application of polyolefin-based resins for food package films which generally require impermeability (barrier) to gas, especially oxygen. For this reason, polyolefin-based resins, along with EVOH superior in oxygen barrier, are formed into food package films, sheets or bottles of multilayer structures through coextrusion, lamination or coating.
With excellent gas barrier and transparency, EVOH is favorably used to provide a gas barrier function upon molding multilayer plastic products. However, recruitment of EVOH is restrained by its cost which is much higher than those of polyolefins. To avoid increasing the cost of such multilayer products, the EVOH layer is made as thin as possible. Thinning the EVOH layer may be a viable option if the multilayer products are maintained uniform in quality. Actually, the opposite is true.
As an alternative to reduce the cost of the multilayer plastic products, there was suggested the compounding of EVOH with inexpensive polyethylene. However, the two components are short of compatibility with each other and thus, are difficult to blend. When a mixture of the two components is used as incompletely blended, the resulting films or sheets appear non-uniform and are poor in mechanical strength. In fact, they are compounded with the aid of a third component, a so-called "compatibilizer" which aids to increase the compatibility therebetween. Now, selection of a compatibilizer for improving the mechanical strength and appearance of products has been an important technical subject.
European Pat. Nos. 15,556 (1980) and 210,725 (1987) and U.S. Pat. No. 4,971,864 (1990) and U.S. Pat. No. 5,356,990 (1994), for example, disclose compatibilizers which comprise polyethylene grafted with polar compounds such as maleic anhydride, asserting that there can be obtained films which show improved oxygen barrier and mechanical properties. However, the products are still poor in appearance such as transparency and thickness variation. Where contents of the compatibilizers are increased to improve the compatibility between EVOH and polyethylene, the resulting resins show poor melt-moldability and oxygen barrier, which must be surmounted for commercialization.